QwertyWEB

                Greasemonkey is a firefox addon which is the perfect tool in which hell lot of scripts can be launched and used to tweak webpages and its exclusively for firefox users . However Greasemonkey scripts can also be made available on Google Chrome using  third party tool. In the same way, here is another application to run Greasemonkey scripts on Safari in Mac OS X  - GreaseKit

Its a SIMBL  plugin, userscript runtime that adds user scripting to Safari, Mailplane, Diet Pibb.app  and all WebKit applications .

First,  install SIMBL.
Copy "GreaseKit" bundle from the downloaded Disk Image.
    * Disk ImageGreaseKit
          * BundleGreaseKit.bundle

And paste the copy in the ~/Library/Application Support/SIMBL/Plugins.

    * HomeYour home
          * FolderLibrary
               * FolderApplication Support
                     * FolderSIMBL
                            * FolderPlugins
                                  * BundleGreaseKit.bundle
Relaunch your Safari.
If the installation is successful, you'll see "GreaseKit" on the menubar! 
You can download this free tool from here : Download GreaseKit